Li1+xAlxTi2-x(PO4)3(LATP) is a promising solid electrolyte for all-solid-state Li ion batteries. In this study, LATP is prepared through a sol-gel method using relatively the inexpensive reagents TiCl4. The thermal behavior, structural characteristics, fractured surface morphology, ion conductivity, and activation energy of the LATP sintered bodies are investigated by TG-DTA, X-ray diffraction, FE-SEM, and by an impedance method. A gelation powder was calcined at 500oC. A single crystalline phase of the LiTi2(PO4)3(LTP) system was obtained at a calcination temperature above 650oC. The obtained powder was pelletized and sintered at 900oC and 1000oC. The LTP sintered at 900~1000oC for 6 h had a relatively low apparent density of 75~80%. The LATP(x = 0.3) pellet sintered at 900oC for 6 h was denser than those sintered under other conditions and showed the highest ion conductivity of 4.50 × 10.5 S/cm at room temperature. However, the ion conductivity of LATP (x = 0.3) sintered at 1000oC decreased to 1.81 × 10.5 S/cm, leading to Li volatilization and abnormal grain growth. For LATP sintered at 900oC for 6 h, x = 0.3 shows the lowest activation energy of 0.42 eV in the temperature range of room temperature to 300oC.